This invention relates to an electric drive system for a vehicle.
Vehicle electric drive systems or AC electric traction drives have been proposed to overcome some of the deficiencies of mechanical transmission systems, such as a limited number of speeds, increased costs of engineering and manufacturing components, and limiting vehicle configuration options. Such an electric drive system is described in U.S. Pat. No. 6,492,785, issued 10 Dec. 2002 and assigned to the assignee of the present application. This system includes an internal combustion engine, an electric motor/generator driven by the engine, a first inverter/rectifier coupled to motor/generator, a bus coupled to the first inverter/rectifier, a second inverter/rectifier coupled to the bus, and a traction motor/generator coupled to an output of the second inverter/rectifier, an operator speed control member, and a controller coupled to the second inverter/rectifier for controlling a current output of the second inverter/rectifier as a function of a position of the speed control member. This system also includes an operator controlled limit control member, and a transducer coupled to the limit control member. The controller receives the limit command signal and limits current supplied by the second inverter/rectifier to the traction motor/generator, so that from an operators viewpoint, in response to manipulation of the operator controlled limit control member, the electric drive system operates and reacts like a mechanical slipping clutch.
Vehicles supplied with such an electric drive system would also necessarily include conventional wheel brakes operated in response to operated controlled brake control devices, such as brake pedals. However, the previously described electric drive system has no provision for coordination with the vehicle brake system. As a result, if an operator would desire to reduce vehicle speed, the operator must not only apply the brakes, he must also separately do something to reduce the output speed of the electric drive system. It would be desirable to provide a vehicle electric drive system which is responsive to or coordinated with the operation of the vehicle brakes.